I. Field of the Invention
The present disclosure relates generally to the fields of chemistry and materials science. More particularly, it concerns metal-organic frameworks, compositions thereof and methods use thereof, including for storing, detecting, and separating of gas and/or liquid molecules.
II. Description of Related Art
Microporous metal-organic frameworks (MOFs) have been rapidly emerging as new type of porous materials for gas storage, separation, sensing and heterogeneous catalysis. The tunable pores and the immobilized functional sites within such microporous MOFs have enabled them to direct specific recognition of certain molecules, and thus for their highly selective guest sorption and separation. The diverse metal ions and/or metal-containing clusters as the nodes and a variety of organic linkers as the bridges to construct the porous coordination polymers (PCPs) by the coordination bonds have led to a series of porous MOFs from ultramicroporous to mesoporous domains. Although thousands of MOFs have been synthesized and structurally characterized over the past two decades, those exhibiting permanent porosity and thus being classified as porous MOFs are still of few percentage. This is primarily due to the labile coordination geometries of the metal ions and/or metal-containing clusters, and the flexibility of the bridging organic linkers which cannot sustain the frameworks under vacuum and/or thermal activation. One efficient strategy to stabilize the PCPs and thus to construct porous MOFs is to make use of rigid clusters (Fang et al., 2006a; Fang et al., 2006b; Bai et al., 2008; Wang et al., 2009), as exemplified in those MOFs with the binuclear paddle-wheel M2(COO)6 (M=Cu2+, Co2+, Ni2+ and Zn2+) and tetranuclear Zn4O(COO)6 as the secondary building units (Eddaoudi et al., 2000). Another strategy to stabilize the frameworks is to make use of the framework interpenetration and/or interwoven to enforce the framework interactions (Ma and Lin, 2009; Kesanli et al., 2005). This approach has been successful in constructing interpenetrated MOFs with higher permanent porosity than their non-interpenetrated analogues (Ma et al., 2007; Ma et al., 2008).
Precise control of pore sizes and pore surfaces within porous materials is very important for their highly selective recognition and thus separation of small molecules, but very challenging and difficult to be realized in traditional zeolite materials (Kuznicki et al., 2001). The situation has been changing since the emerging of the new type of porous materials, so-called microporous metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) over the past two decades. This is because the pores within such porous MOFs, particularly those within isoreticular metal-organic frameworks whose structures are pre-determined by the coordination geometries of the secondary building blocks (SBUs), can be systematically modified simply by the change of different organic bridging linkers and the control of the framework interpenetration (Deng et al., 2010; Chen et al., 2010; Ma et al., 2010; Horike et al., 2009). Furthermore, the pore surfaces within such porous MOFs can be functionalized by the immobilization of different recognition sites such as the open metal sites, the Lewis basic/acidic sites, and chiral pockets to direct their specific recognition of small molecules (Britt et al., 2009; Shimomura et al., 2010; Rabone et al., 2010; Devic et al., 2010; Seo et al., 2000; Morris and Bu, 2010; Chen et al., 2009; Yang et al., 2009; Xie et al., 2010). In fact, to systematically tune the micropores to induce their size specific encapsulation of small gas molecules and to immobilize functional sites to direct their different interactions with the substrates, various series of microporous metal-organic framework materials have been emerging as the promising microporous media for the recognition and separation of small molecules (Kitaura et al., 2004; Chen et al., 2004; Cho et al., 2006; Liu et al., 2010; Murray et al., 2010; Ma et al., 2009; McKinlay et al., 2008; Dubbeldam et al., 2008; Chen et al., 2006; Finsy et al., 2008; Bae et al., 2010; Zhang et al., 2008; Dybtsev et al., 2004; Li et al., 2009; Vaidhyanathan et al., 2006; Nuzhdin et al., 2007; Dybtsev et al., 2006; Chen et al., 2008).
Kitagawa pioneered the research on construction of porous mixed-metal-organic frameworks (M′MOFs) by making use of M-Salen metalloligands in 2004 (Kitaura et al., 2004; Chen et al., 2004). Such a novel approach eventually led to few porous M′MOFs for heterogeneous asymmetric catalysis and enantioselective separation (Ma et al., 2010; Cho et al., 2006; Liu et al., 2010). More recently, this metalloligand or pre-constructed building block approach has been successfully developed to construct porous metal-organic frameworks, and realized the first such mixed-metal-organic framework (M′MOF) Zn3(BDC)3[Cu(SalPyen)].(G)x (M′MOF-1; BDC=1,4-benzenedicarboxylate; SalPyenH2=Schiff base condensed from 5-methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde and ethylenediamine; G=guest molecules) with permanent porosity clearly established by both gas and vapor sorption (Chen et al., 2008). This new M′MOF approach has provided us with a new dimension to tune and functionalize the micropores within this series of isoreticular M′MOFs by (a) the incorporation of different secondary organic linkers, (b) the immobilization of different metal sites other than Cu2+, (c) the introduction of chiral pockets/environments through the usage of chiral diamines, and (d) the derivatives of the precursor through the usage of other organic groups such as t-butyl instead of methyl group, and thus to explore novel functional microporous M′MOFs for their recognition and separation of small molecules.
Although thousands of MOFs and M′MOFs have been synthesized and structurally characterized over the past two decades, the ones with open metal sites are still relatively few (Chen et al., 2010; Dinca and Long, 2008), this is mainly because such open metal sites are typically very reactive and tend to bind the atoms from the neighboring ligands to form the condensed structures. Also, few MOFs have been shown to be useful for selective sorption, separation and/or sensing of guest molecules. Accordingly, identifying and developing new MOFs and/or M′MOFs that exhibit one or more of these useful properties is desirable.